1. Field of the Invention
This invention relates to hydraulically fracturing subterranean formations having an injection means in fluid communication with the subterranean formation. Fracturing is effected with an aqueous fracturing fluid containing a crosslinked polymer.
2. Description of the Prior Art
The productivity or injectivity of a well or formation may be greatly reduced by contamination with waxy occlusions, casing cement, drilling mud, emulsion blocks, low permeability of the formation rock, etc. These blockages may be overcome by injecting a fluid into a well to hydraulically fracture the formation at a sufficient rate and pressure to overcome the tensile strength of the formation and the overburden pressure. This causes cracks extending from the wellbore out into the formation and permits the flow of hydrocarbons and other liquid and gaseous fluids.
Desirable fracturing fluid properties include stability under formation conditions, high viscosity and low fluid loss and low friction loss during injection into the formation. Crosslinked polymer solutions possess some if not all of these properties.
Patents representative of the prior art include the following:
U.S. Pat. No. 3,542,044 to Hansen et al: Incorporating polyacrylamide having a molecular weight of at least 3,000,000 in a fracturing fluid reduces energy loss during the pumping of the fluid. The polyacrylamide acts as a friction reducing and dispersing agent.
U.S. Pat. No. 3,537,525 to Sarem: Friction loss during pumping is reduced by incorporating an acrylic acid-acrylamide-diacetone acrylamide terpolymer into a fracturing fluid in concentrations up to 500 ppm. The terpolymer provides better friction reduction than is obtained using a partially hydrolyzed polyacrylamide.
U.S. Pat. No. 3,370,650 to Watanabe: A suspension of finely divided particles of water-insoluble, oil-soluble homogeneous solid solution of wax and polymer in an aqueous solution of a partially hydrolyzed, high molecular weight polyacrylamide is used for fracturing. The polyacrylamide has 12-67 percent of the original amide groups hydrolyzed to carboxyl groups.
U.S. Pat. No. 3,254,719 to Root: The pressure drop due to flow of a fracturing fluid is reduced by 0.005-4 weight percent of an acrylamide polymer. The polymer can be a long chain polymer of ethylene oxide having a molecular weight of one to ten million or a copolymer of acrylamide with other monoethylenically unsaturated monomers copolymerizable therewith.
U.S. Pat. No. 2,842,338 to Davis et al: A drilling fluid is obtained by the in situ crosslinking of polyacrylic acid with a polyvalent cation.